1. Field of the Invention
The present invention relates to a high-pressure fuel pump control device for an engine, and more particularly to a high-pressure fuel pump control device capable of variably adjusting a discharge amount of high-pressure fuel that is fed under pressure to a fuel injector valve.
2. Description of the Related Art
From the viewpoint of environmental protection, there are at present a demand in the field of automobiles for reducing particular substances contained in automobile exhaust gas, such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), i.e., for improving exhaust emission characteristics and enhancing fuel economy. To meet such a demand, a direct injection engine (in-cylinder injection engine) is under development. In the direct injection engine, improvements in exhaust emission characteristics and hence in engine output are intended by directly injecting fuel from a fuel injector valve into a combustion chamber of each cylinder so that the fuel is injected in smaller particle size from the fuel injector valve and combustion of the injected fuel is promoted.
To make smaller the particle size of the fuel injected from the fuel injector valve, some means for pressurizing the fuel to a high-pressure level is required, and a high-pressure fuel pump for feeding the high-pressure fuel to the fuel injector valve is used as such a means.
One example of known high-pressure fuel pumps comprises a pressurization chamber, a plunger for pressurizing fuel in the pressurization chamber, a fuel passage valve (inlet valve) disposed in the pressurization chamber, and an actuator for actuating the fuel passage valve. In a discharge stroke (plunger rising stroke), the fuel passage valve is closed to feed the fuel under pressure to a common rail (fuel accumulation chamber).
In control of such a high-pressure fuel pump, the timing of closing the fuel passage valve is set depending on the fuel pressure, and a solenoid drive signal (pulse), i.e., an actuator drive signal, is outputted under angle or time control at the set timing on the basis of a REF signal produced from both a cam angle signal and a crank angle sensor, thereby closing the fuel passage valve.
Just after the start of engine operation (i.e., the start of cranking), however, the phases of a cam angle and a crank angle are not definite, and the REF signal is not produced. Accordingly, it is impossible to set the timing of closing the fuel passage valve. For that reason, various techniques are proposed on control of the high-pressure fuel pump just after the operation start, i.e., for a period from the operation start to a point in time at which the phases of the cam angle and the crank angle become definite.
For example, JP-A-2001-182597 (pp. 1–24, FIGS. 1 to 22) discloses a technique of outputting the actuator drive signal (pulse) at least two times during a period from recognition of the crank angle signal to the point in time at which the phases of the cam angle and the crank angle become definite, i.e., during a period from the operation start to the point in time at which it becomes possible to output the actuator drive signal in a predetermined crank angle phase.
Also, JP-A-2003-41982 (pp. 1–13, FIGS. 1 to 9) discloses a technique of, at operation start of an in-cylinder injection engine including a high-pressure fuel pump operatively coupled to a crankshaft, performing duty control of power supply to a spill valve of the high-pressure fuel pump at a cycle of very short time before the timing at which the crank angle phase becomes definite, and stopping the fuel pressure control with such duty control after the crank angle phase has become definite. Thereafter, the timing of starting the spill valve to close is set to predetermined timing, and the spill valve is closed at the set predetermined timing of starting the valve closing, to thereby boost the fuel pressure. The timing of switching the fuel pressure control from the former mode to the latter mode is set so as to cover a period from lust after the start of a discharge stroke of the high-pressure fuel pump to the timing that has been computed as the predetermined timing of starting the valve closing.